(i) Field of the Invention:
The present invention relates to an adiabatic separator for the separation by condensation of a portion of a homogeneous gas or of a condensible gas from a carrier gas, more particularly for the separation of water vapour from industrial flue gases.
This invention also relates to a process of such separation and in particular to a process of removal of water vapour from (dehumidification of) exhaust-flue gases especially where these latter also contain the pollutant sulphur dioxide which may be simultaneously removed by its dissolution in the condensed water, prior to discharge of the flue gases into the atmosphere.
(ii) Description of the Prior Art:
The blades of steam turbines, used for instance in nuclear power generators, suffer significant mechanical erosion ("pitting") problems owing to the impingement of condensed water droplets on the fast rotating turbine blades. This erosion requires that the turbine blades be replaced annually at high cost. It would be desirable therefore to supply such turbines with a "higher quality" steam, i.e. steam at a slightly higher temperature than usual in order to reduce the amount of droplets forming by condensation within the turbines.
Another branch of the power generation industry concerns power boilers.
The majority of power boilers in North America are coal fired units, in which ground coal is burned with air, producing hot combustion ("flue") gases.
From the initial combustion temperature of approximately 3500.degree. F., the flue gas loses its temperature towards the boiler's exit and leaves the boiler proper at approximately 300.degree. to 400.degree. F. After leaving the boiler's periphery, the flue gas enters a stack and is discharged directly to the atmosphere.
These high temperatures allow considerable quantities of air pollutants to be carried into the atmosphere with the flue gas. The most prominent among all air pollutants are solid particles of coal ash and gaseous sulphur dioxide.
Contamination of the atmosphere with sulphur dioxide has proved to have devastating environmental effects as it is directly responsible for so-called "acid rain".
Ever stringent air pollution control requirements enacted by governments in recent years, have forced industries to reduce the level of solid pollutants discharged into the atmosphere. The technology that has been developed for this purpose involves a so-called "scrubbing" process.
In such an arrangement, flue gases leaving the power boiler pass through a special chamber called a "scrubber" where large quantities of cold water are injected into the flue gas stream causing coagulation of the solid ash particles. These particles subsequently collect in the bottom of the scrubber and thus are effectively removed from the gas stream. After being removed from the scrubber the wet ash is then transported to a dump site for permanent disposal.
The scrubbing process appears to be very effective in removal of solid particles from the flue gas stream, but has some undesirable side effects.
A significant portion of the cold water sprayed inside the scrubber evaporates after coming in contact with the hot flue gases. This effectively reduces the temperature of the flue gases and leaves them saturated with moisture. Upon leaving the stack the wet flue gas comes into direct contact with cold ambient air causing instant precipitation of the moisture resulting in a very environmentally objectionable plume of white "smoke".
An additional drawback of the scrubbing process is its inability to reduce the content of sulphur dioxide in the gas stream. Instead the sulphur dioxide tends to remain in gaseous form on leaving the scrubber. This is largely because the temperature of the flue gas is still too high for dissolution of sulphur dioxide in liquid water.